`IsComplete` may check `requires`, making checking before writing to a 0-initialized buffer difficult.

In the C++ runtime if a type has a `requires` clause and that field is used in determining the size of the struct, `IsComplete` appears to check that `requires` clause. This means a generic approach of 0-initializing a buffer then checking `IsComplete` breaks for structs that have fields that exclude 0, for instance.

Workarounds involve either leaving it unchecked and manually confirming (defeating the purpose of checks like `IsComplete`) or splitting definitions into fixed-size portions and variable-sized portions.

We should evaluate whether `IsComplete` should ignore the `requires` for these fields, or if there's a good reason we need to ensure the consistency of these fields, potentially provide a verifier that ensures that all fixed-size, fixed-location portions of the struct are safe to write to, allowing the client code to call `IsComplete` once they've initialized those to ensure the entire struct is safe to write to.